Membrane separation technologies are more and more used in water treatment for the production of water for human consumption and for use in industry. Major membrane processes in water treatment are microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). Microfiltration and ultrafiltration are filtration processes characterized by extremely high removal rates of solid material (particulate and colloidal matter) present in the water, whereas nanofiltration and reverse osmosis allow the removal of compounds that are dissolved in the water.
Compared to conventional water treatment processes, membranes offer several advantages, especially a better and constant quality of the treated water.
A major challenge for the implementation of membrane processes is the control of fouling of the membranes.
Common types of membrane fouling are:                fouling by particles and colloids that deposit on the membrane surface        scaling, i.e. precipitation of sparingly soluble salts        organic fouling, i.e. adsorption of organic compounds on the membrane surface        biofouling, i.e. excessive growth of a biofilm at the membrane surface        
In reverse osmosis and nanofiltration, most commonly the separative layer of the membrane is made of a polyamide with a very limited resistance to oxidants like chlorine. Today the module type generally used in reverse osmosis and nanofiltration units is the so-called spiral wound module. A second type of commonly used reverse osmosis and nanofiltration membranes is hollow fibers.
Among the different types of fouling observed on plants using such polyamide reverse osmosis or nanofiltration membranes, biofouling is the most frequent one. Membrane biofouling causes increased energy consumptions due to increased pressure requirements. A further concern is the increase in required membrane frequency resulting in production losses due to increased downtime and in reduced membrane life. Also very high pressure losses across the modules (between feed and concentrate) may cause mechanical damage of the module. In all cases the consequence of biofouling is an increase in costs per amount of produced or treated water.